This application is related to U.S. Pat. No. 6,286,892, which issued on Sep. 11, 2001.
1. Field of Invention
The present invention relates generally to controlling drag on ground vehicles and, more particularly, to the passive control of drag on ground vehicles using porosity.
2. Description of the Related Art
Previous devices for controlling drag on ground vehicles have involved active devices that attempted to inhibit separation on the base, or aft portion, to create a predetermined best situation. These devices consist of flaps, turning vanes, vortex generators, and a wide range of suction and blowing concepts which add considerable weight to the overall vehicle weight and increase fuel consumption.
It is accordingly an object of the present invention to control drag on ground vehicles.
It is another object of the present invention to achieve the foregoing objects with a passive device.
It is a further object of the present invention to achieve the foregoing objects with minimal spatial and mass requirements.
It is yet another object of the present invention to accomplish the foregoing objects in a simple manner.
Additional objects and advantages of the present invention are apparent from the drawings and specification that follow.
According to the present invention, the foregoing and additional objects are obtained by providing a drag reduction device for use on a ground vehicle. This device can consist of a porous outer skin having a thickness between about {fraction (1/16)} inch (0.16 cm) and 1 inch (2.54 cm), preferably between {fraction (1/16)} inch (0.16 cm) and xc2xc inch (0.635 cm), which is offset from the trailing surface and affixed to the trailing surface of the ground vehicle (e.g., the outer surface of the doors). The porous outer skin is separated from the trailing surface of the ground vehicle by a distance equal to at least the thickness of the porous skin (e.g., 0.25 inch [0.635 cm]or more), thereby forming a plenum therebetween. The surface porosity of the porous outer skin can be between about 10 and 20 percent. The porous outer skin may be fabricated from a porous material or by creating a number of perforations in a solid material. Additionally, it is also within the scope of the present invention tat a porous outer skin also be attached to one or more of the normal exterior sides and/or top surfaces of the trailer. If the perforation method is used, the maximum dimension of the perforations can be about 0.25 inch (0.635 cm) on the sides and top of the ground vehicle and about 0.50 inch (1.270 cm) on the trailing surface of the ground vehicle.
Alternatively, the typical existing trailing surface of the ground vehicle may itself be porous. Again the surface porosity can be between about 10 and 20 percent. The porosity may be caused by perforating the ground vehicle""s existing trailing surface, and, depending on the thickness of the trailing surface, the maximum dimension of the perforations can vary, but it is preferably about 0.125 inch (0.3175 cm) for a trailing surface with a thickness of 0.25 inch (0.635 cm) or more. This perforating could possibly be done either during manufacture of the door or panel, or added later to a vehicle that has already been manufactured. For example, the vehicle""s existing trailing surface can be the exterior surface of a rear door or doors, or it may be a full rear surface, (e.g., a non-openable rear panel) on the vehicle. It is within the scope of the present invention that virtually any variety of rear xe2x80x9cdoorxe2x80x9d (overhead, side by side, etc.) might be utilized, so long as an interior panel or surface is available to form a plenum between the outer and inner surfaces, to thus permit air flow therebetween.
Similarly, in another possible embodiment of the present invention, rather than attaching a porous surface to the sides or top of a vehicle, alternatively, a portion of the existing exterior surface of the vehicle body itself may be porous, for example, the normal exterior side and/or top surfaces of a trailer could be perforated. The perforating of the outer trailer surface can, for example, either be done during the original manufacture of the vehicle, or perforations could potentially be added after manufacture. Additionally, if the exterior surface of a trailer is perforated, then an inner non-perforated surface (or surfaces) should be positioned substantially parallel to the porous outer surface or skin. This internal surface can be separated from the side or top surfaces of the ground vehicle by a distance equal to at least the thickness of the porous skin (with a minimum of about 0.25 inch) to form a plenum between the porous and non-porous surfaces. In at least one embodiment, the perforations can extend a substantial distance from the trailing surface of the vehicle along the side(s) and/or top, for example, between about 5 and 10 percent of the total length of the trailer can be perforated, and the porosity can be between about 10 to 20 percent of the perforated surface area.